The present invention relates to a semiconductor device that includes a fluorine-containing organic film having a low relative dielectric constant and a method for fabricating the same.
With recent remarkable progress in semiconductor process technology, finer semiconductor elements and metal interconnections with higher integration have been pursued. With this trend toward finer size and higher integration, signal delay at metal interconnections has come to greatly influence the operation speed of semiconductor integrated circuits.
In the above situation, desired is a technique of forming a fluorine-containing organic film (fluorocarbon film) that contains carbon atoms and fluorine atoms as main components and has a relative dielectric constant lower than that of an inorganic film such as a SiO2 film or a SiOF film.
A fluorine-containing organic film has a relative dielectric constant of about 2, which is lower than the relative dielectric constant of a SiOF film (about 3.5 to about 3.8). Accordingly, by depositing such a fluorine-containing organic film between metal interconnections or on the top surfaces of metal interconnections, signal delay at the metal interconnections can be reduced.
However, the fluorine-containing organic film deposited using a material gas containing fluorine described above is disadvantageously poor in denseness and thus insufficient in mechanical strength, heat resistance, chemical resistance, and the like.
In order to solve the above problem, Japanese Laid-Open Patent Publication No. 10-199976 proposes a method for densifying a fluorine-containing organic film to improve mechanical strength, oxidation resistance, and heat resistance in the following manner. A copolymer of a polytetrafluoroethylene resin or a cyclic fluorine resin and siloxane is dissolved in a fluorocarbon solvent. The resultant solution is applied to a substrate while rotating, to obtain a fluorine-containing organic film. The resultant fluorine-containing organic film is then subjected to annealing where the film is kept in an atmosphere of an inert gas such as nitrogen gas at a temperature of 400xc2x0 C. for 30 minutes.
By the annealing of the fluorine-containing organic film, the film is densified and thus the mechanical strength improves as described above. However, since fluorine atoms in the film are volatilized by the annealing, the relative dielectric constant of the film increases. That is, if no annealing is performed, the relative dielectric constant is low, but the mechanical strength is poor. If annealing is performed, the mechanical strength improves, but the relative dielectric constant becomes high. In other words, reduction in relative dielectric constant and improvement in mechanical strength are completely in the trade-off relationship where selection of either one only is allowed.
In view of the above, the object of the present invention is allowing control of the amount of fluorine atoms contained in a fluorine-containing organic film to balance reduction in relative dielectric constant with improvement in mechanical strength.
In order to attain the above object, the first method for fabricating a semiconductor device of the present invention includes the step of: depositing a fluorine-containing organic film having a relative dielectric constant of 4 or less on a semiconductor substrate using a material gas containing fluorocarbon as a main component in a reactor chamber of a plasma processing apparatus, wherein in the deposition of a fluorine-containing organic film, a scavenger gas for scavenging fluorine constituting the fluorocarbon is mixed in the material gas, and the proportion of the mixed scavenger gas in the material gas is changed to adjust the mechanical strength and relative dielectric constant of the fluorine-containing organic film.
According to the first method for fabricating a semiconductor device, the mechanical strength and relative dielectric constant of the fluorine-containing organic film are adjusted by changing the proportion of the scavenger gas mixed in the material gas. Therefore, it is possible to reduce the relative dielectric constant by relatively increasing the amount of fluorine atoms in the film for a fluorine-containing organic film giving high priority to reduction in relative dielectric constant. Contrarily, it is possible to increase the mechanical strength by relatively decreasing the amount of fluorine atoms in the film for a fluorine-containing organic film giving high priority to improvement in mechanical strength. In other words, by changing the proportion of the scavenger gas mixed in the material gas, reduction in relative dielectric constant and improvement in mechanical strength are balanced.
The second method for fabricating a semiconductor device of the present invention includes the steps of: depositing a first fluorine-containing organic film having a relative dielectric constant of 4 or less on a semiconductor substrate using a first material gas in a reactor chamber of a plasma processing apparatus, the first material gas containing fluorocarbon gas mixed with a relatively small amount of a scavenger gas for scavenging fluorine constituting the fluorocarbon; and depositing a second fluorine-containing organic film on the first fluorine-containing organic film using a second material gas in the same reactor chamber, the second fluorine-containing organic film being superior in mechanical strength to and higher in relative dielectric constant than the first fluorine-containing organic film, the second material containing the fluorocarbon gas mixed with a relatively large amount of the scavenger gas.
According to the second method for fabricating a semiconductor device, the first fluorine-containing organic film is deposited using the first material gas containing a scavenger gas for scavenging fluorine constituting the fluorocarbon in a relatively low mixture proportion, while the second fluorine-containing organic film is deposited using the second material gas containing the scavenger gas in a relatively high mixture proportion. Therefore, the first fluorine-containing organic film has a relatively low mechanical strength but has a relatively low relative dielectric constant, while the second fluorine-containing organic film has a relatively high relative dielectric constant but has a relatively high mechanical strength. In this way, by only changing the mixture proportion of the scavenger gas, it is possible to form the first fluorine-containing organic film having a relatively low relative dielectric constant and the second fluorine-containing organic film having a relatively high mechanical strength.
In the first or second fabrication method, the scavenger gas is preferably CO gas. This ensures scavenging of fluorine constituting the fluorocarbon.
In the first or second fabrication method, the fluorocarbon is preferably C5F8, C3F6, or C4F6.
Using the above fluorocarbon, the number of free fluorine atoms in the deposited fluorine-containing organic film decreases. This densifies the fluorine-containing organic film and also improves the adhesion thereof. In addition, C5F8 gas, C3F6 gas, and C4F6 gas less easily cause global warming compared with other perfluorocarbon gases.
In the second fabrication method, the first fluorine-containing organic film is preferably deposited between a plurality of metal interconnections formed on the semiconductor substrate.
With the above construction, since the relative dielectric constant of the first fluorine-containing organic film is low, the capacitance at the metal interconnections is small. In addition, the second fluorine-containing organic film deposited on the first fluorine-containing organic film has a high mechanical strength. Thus, compatibility between reduction in capacitance at the metal interconnection structure and improvement in mechanical strength is attained.
In the second fabrication method, the first material gas may not contain the scavenger gas. This ensures the reduction in the relative dielectric constant of the first fluorine-containing organic film.
Preferably, the second fabrication method further includes the step of: densifying the second fluorine-containing organic film by exposing the second fluorine-containing organic film to plasma of a rare gas in the same reactor chamber.
By the above step, the mechanical strength of the second fluorine-containing organic film further increases, and the heat resistance and chemical resistance thereof further improve.
The semiconductor device of the present invention includes: a plurality of metal interconnections formed on a semiconductor substrate; a first fluorine-containing organic film deposited at least between the plurality of metal interconnections; and a second fluorine-containing organic film deposited on the first fluorine-containing organic film, wherein the amount of fluorine atoms contained in the second fluorine-containing organic film is smaller than the amount of fluorine atoms contained in the first fluorine-containing organic film.
According to the semiconductor device of the present invention, the first fluorine-containing organic film has a relatively low mechanical strength but has a relatively low relative dielectric constant, while the second fluorine-containing organic film has a relatively high relative dielectric constant but has a relatively high mechanical strength. Thus, compatibility between reduction in capacitance at the metal interconnections and improvement in mechanical strength is attained.